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This afternoon I dragged my brother out of the house on his day off to help me with an experiment. You may notice his collar turned up in the following pictures, that’s to keep out the rain that decided to suddenly descend on us when we got to the woods, and then the sleet that followed. He didn’t run away. Have I mentioned how lucky I am to have a brother who’s such a good sport? Very lucky!

Anyway. Today’s experiment was about properly understanding focal length. Not the science behind it, that’s for someone a little more technically minded (I bet my brother could explain it to me after a few minutes of research), but rather about the effect our focal length choices have on the images we take.

I’m aware that I love the look of certain lenses (my beloved 85mm 1.8 for example), while others just don’t inspire me so much, but I’ve never shot with each lens in turn to really understand what they do to the scene in front of me.

For this experiment I set up the camera on a tripod so it would remain at an even height throughout and I asked my brother to stand in one spot without moving an inch. As well as the angle of field, I wanted to demonstrate the effect that focal length has on depth of field, in other words the way the background softens with longer focal lengths, so I set the camera to stay at f/5.6 no matter which lens I was using. In this way the background would only be affected by the focal length and not the more usual method of changing the aperture. The only exposure setting I adjusted while shooting was the shutter speed to work with the light when it changed slightly due to the sun.

Before I show you the pictures it’s worth mentioning that I’m shooting on a Canon 550D with a multiplier of about 1.6, so technically all these focal lengths are the equivalent of slightly higher than I’ve labeled them (30mm becomes 48mm, 85mm becomes 136mm etc) and the same lenses on another body may look a little different, but the relative difference between each focal length remains exactly the same.

With each focal length change I had to take a step or two back to keep the composition as similar as possible. And this is what I got…

And here is the widest photo next to the longest photo for a comparison:

(Photos taken at: 1/320, f/5.6, ISO 800 and: 1/320, f/5.6, ISO 800)

Looking at these it’s easy to see why telephoto lenses are often considered “portrait lenses”. There is less distortion on his face, and the soft background even at f/5.6 makes the subject become the main focus of the image.

But my favourite part of this experiment was finally really understanding what it means when you hear that telephoto lenses “compress” the foreground and background. I’ve understood it in theory but haven’t seen a before/after example in my own photos before.

Let’s look at the side by side again:

(Photos taken at: 1/320, f/5.6, ISO 800 and: 1/320, f/5.6, ISO 800)

Look at the tree over his shoulder in the first photo, then look at it again in the second photo, it seems to have moved forward about a dozen or so metres, or in other words, it has been compressed! I had no idea quite how dramatic the effect can be, but now that I’m aware of it I will certainly be using this knowledge while planning future shoots.

I’m planning more forays into the world of focal length. In the meantime, what’s your favourite lens or focal length? Which do you not like so much? Email or comment below and let me know!

My photo was picked for Group 1 of the Landscape assignment over at PioneerWoman! As usual, she’s put together a wonderful selection, the best out of thousands of beautiful submissions. I’m thrilled to somehow be in there amongst them. Go and take a look at the gorgeous landscape photos there! Group 2 is now up as well.

Have you ever been completely over the moon about discovering something and tried to explain it to someone else, only to then have to explain why it’s “sooooo amazing!!”?

That was me last night trying to explain to my family how thrilled I was to discover back-button autofocus on my Canon 450D. I’d never heard of it before, I don’t know if that’s due to me missing something, or just that it’s not commonly known. But in my view it’s the greatest invention since… since the thing before they invented sliced bread.

The site I found for instructions is specific to Canon EOS. A quick search turned up some Nikon users discussing it, although I don’t know which models implement this. Here’s the link for Canon users.

I recommend reading through once quickly before trying to change anything as the article discusses back-button auto focus a lot, but doesn’t explain how to change any settings until near the very end. Also, the actual wording in your custom functions menu are likely to be different than the example ones on the site. You may understand it all straight away, or you may be like me and have to play with them until it makes sense and does what you want.

That’s great… but what is it?

This is my cue to make a confession: I rarely use manual focus.

I’d love to have the confidence in my focusing skills but I tend to shoot fast, and often miss shots if I stop to mess with focusing. Like any photographer, I hate to miss out on photos because they’re badly focused. And modern auto-focus is often so quick and crisp that it seems a shame to waste it. Or maybe I’m just lazy and making excuses. Either way, I usually use auto-focus.

The problem with auto-focus is that I often find my camera’s focus drifting between the time I press the shutter button halfway to focus, and all the way to release the shutter. This is especially true when I try to lock focus on an object and re-compose the image before taking the photo. And if I have a stationary subject I still have to re-focus every time I take my finger off the shutter button. Well no more.

Back-button AF takes the focus control from the shutter button and puts it on a button on the back of the camera instead. Changing these settings has turned what was my AE lock button into a dedicated focus button, and I have set my half-pressed shutter button to be AE lock, so that feature is not only still available, but is far more accessible and useful to me now.

Once I’ve focused I can now recompose to my heart’s content, and take as many photos as I like without ever touching the focus. The Canon site gives a lots of examples of where this can be useful.

It takes some getting used to, but I love it already and doubt I’ll be going back to standard AF in a hurry. If you have a Canon SLR (or any other that has this function) give it a try and see if you like it!

Oh, and one last point. This function is only activated in the “creative zone” modes (P, Av, Tv & M), so if you click the dial to the “green box” auto mode, you can hand it over to anyone to use without having to explain how your focus works. Handy.